It is known in the art to oxidize phenol to benzoquinone, e.g., para-benzoquinone with oxygen in the presence of a copper ion catalyst and such a process is disclosed in U.S. Pat. No. 3,987,068. In that patent the oxidation is carried out in a nitrile solvent using a complex formed from the copper catalyst and the solvent and the operating conditions are said to be at temperatures of from about 0.degree. to 100.degree. C. and a partial pressure of oxygen of from about 7 to 200 (preferably 14 to 100) atmospheres. As pointed out in U.S. Pat. No. 3,987,068, yield of quinone product increases with increased partial pressure of oxygen and it appears from the data therein that partial pressures of oxygen above about 100 atmospheres are required in order to achieve conversions of phenol to p-benzoquinone on the order of about 75%. Such pressures are too high to be useful in an economical commercial process because they require special equipment of high capital cost.
U.S. Pat. No. 3,870,731 relates to the oxidation of phenols to benzoquinones in the presence of copper salts as catalyts where the catalyst is promoted with thiocyanate, cyanate, cyanide and halogen ions. In such reactions a solvent such as water is disclosed and other polar solvents soluble or miscible with water may be used. Such solvents are exemplified as certain amides, alcohols, and sulfoxides.
U.S. Pat. No. 4,208,339 discloses a process for the preparation of p-benzoquinone by oxidation of phenol in the presence of cuprous or cupric ions in the presence of a metal in the metallic form in a nitrile, amide, alcohol or sulfoxide solvent. Reaction rate is said to be increased by including an alkali metal or alkaline earth metal halide.
In South African patent publication No. 78/5012 on the oxidation of phenol to p-benzoquinone with a cuprous or cupric catalyst, the presence of a reducing agent for cupric ion to cuprous ions is said to give improved yield and/or improved conversion. Such reducing agents are exemplified by diphenol, a substituted alkylphenol, an aliphatic aldehyde, an aliphatic ketone of 3 to 6 carbon atoms, or an aliphatic or cycloaliphatic olefin or diolefin.